Continuous ink jet printing involves the formation, from a continuous cylindrical ink stream being discharged from an appropriately sized orifice in a nozzle assembly, of tiny equally spaced and sized ink droplets, which are then individually redirected to strike a target area at specific locations suited to form an intended message. To achieve this droplet flow stream, the liquid ink in the nozzle assembly is subjected to ultrasonically pulsated pressures created by utilizing both a steady moderate pressure system and a piezoelectric crystal oscillator associated with and coupled to the nozzle assembly. Utilizing suitable synchronizing controls, each ink droplet will then be left uncharged or will be selectively charged electrically to a specific but varied potential upon passing a charging electrode or ring proximate the ink droplet stream. Thereafter, each charged droplet will be passed proximate electrically charged deflection plates, to be redirected laterally to impact then against the media (which typically will be paper, plastic, metal, etc. moving laterally past the nozzle) and effectively print thereon one or more lines of meaningful letters, numbers, symbols or like characters. The uncharged droplets will strike a collecting gutter for delivery back to the ink reservoir and reuse.
FIG. 1 illustrates schematically the above-noted ink flow loop 12 and components including ink reservoir 14, pump 16, pressure regulator 18, nozzle assembly 20, droplet charging electrode 22, droplet deflecting plates 24, ink return collector 26; and the ink discharge stream 27 and the diverted ink droplet stream 28 therefrom that is to impact against the media 30. Piezoelectric oscillator 32 is also shown associated with nozzle assembly 20, as is thermoelectric heater/cooler 36 in the ink flow loop 12. Moreover, conventional controls including respective feedback vibration and temperature sensors 33, 37; vibration and temperature power input setting devices 34, 38; and vibration and temperature comparators 35, 39 can be provided for sensing the ink vibrations and temperatures associated with the discharged ink droplets and for adjusting power to the oscillator and/or heater/cooler in an attempt for stabilizing the resulting desired printing pattern. However, such feedback sensors for the comparative compensating systems typically have been located remotely from the nozzle assembly (not as shown, inasmuch as that shown represents the inventive sensor locations), resulting overall in inaccurate and/or unreliable corrections.
This invention relates to an improved nozzle assembly 20, specifically suited for overcoming drawbacks, problems or difficulties experienced in existing continuous ink jet printing systems.
Specifically, all conventional nozzle assemblies utilize a very small orifice (in the range between 36-80 microns) so that orifice clogging with reduced print quality thereafter is a common threat. A filter commonly is mounted in the nozzle assembly upstream of the orifice to help prevent particles from making their way to the orifice. Clogging particles can be present due to sloppy manufacturing, such as being left between the filter and the orifice, or can be generated as precipitates of ink salts due to charging currents used while printing. Further, a properly functioning filter over time will become blocked, and quite quickly in dusty atmospheres containing high concentrations of particulate. As the filter is located internally of the nozzle assembly, filter replacement thus requires the nozzle assembly to be disassembled, which when attempted in the field in most cases is very difficult.
One current continuous ink jet printing system attempts to clean the nozzle orifice without dismantling it, and provides a port open to the nozzle interior between the filter and orifice, the port being closed during normal printing operation. However, when it is desirous to clean a clogged orifice, a suction is applied to the port which serves to withdraw ink through this port and from the nozzle interior as well as makeup air and/or solvent drawn backward through the orifice. However, blockage removal is not guaranteed, particularly blockage caused by fibers which are most difficult to remove.
One existing nozzle assembly supports the orifice in a removable plate, so that upon clogging, the entire orifice plate can be removed, to allow for orifice cleaning and/or replacement. The problem with this approach is that the orifice plate is held gaped from an adjacent face of the nozzle body, with an O-ring surrounding the ink flow path snugged therebetween to preclude leakage, and adjusted by three triangularly arranged screws to align the discharging ink flow stream accurately on target. This alignment task requires schooling and/or practice, so that in the field orifice replacement is difficult and/or can only be done by qualified technicians.
Moreover, different printing operations or systems might need different sizes of nozzle orifice, but as in the field nozzle orifice replacement is so difficult, time consuming, or technically demanding, a user might commonly stock in inventory different printing heads (at great expense per print head), each having a specific needed nozzle orifice size for the specific printing operation or system.
Further, although the sonic vibration level produced by the piezoelectric oscillator can be set, based on system hardware and ink stream printing requirements, to breakdown the cylindrical ink stream discharge into the properly sized and separated droplet stream, even minor changes from this vibration level or in the ink temperature might cause varied or unstable printing patterns. More specifically, physical ink properties (surface tension being the most prevalent) and sonic coupling of the powered driving oscillator signal via the nozzle body to the ink contained therein typically change with changes in the ink temperature. As noted, efforts to stabilize the ink flow include feedback sensors and controls effective for modifying the input power to the oscillator and/or the ink heater/cooler; but such can be inconsistent or inaccurate due to the remote locations of the sensor(s) from the powering oscillator.
This invention relates to continuous ink jet printing systems, and more particularly, to an improved nozzle assembly used therein.
An object of this invention is to provide a continuous ink jet printing system nozzle assembly that an operator can service on site, such as for removing the nozzle orifice for cleaning and/or for changing to a different needed size, and/or for removing the particle filter when necessary and replacing it with a new one, all quite quickly and easily and without any need for realigning the discharging ink flow stream.
Another object of this invention is to provide a continuous ink jet printer system nozzle assembly having structure selectively holding one or more sensors in close proximity to the flowing ink stream, for detecting ink vibrations and/or temperatures and/or other property, whereby accurate and instantaneous feedback might be available that with suitable conventional controls can modify the sensed ink property and thereby stabilize the set discharging ink flow stream or printing pattern.
A specific feature of this invention is a continuous ink jet printer nozzle assembly defining a through passage for the ink flow, the nozzle assembly and through passage being comprised of separate main ink driver and orifice subassemblies separably held relative to one another by the driver subassembly having an axially extended exteriorly open cavity or bore for receiving and providing, with an O-ring therebetween, a sealed mechanically snug self-aligning fit for said orifice subassembly, for allowing easy and accurate in the field operator servicing removal and replacement of the orifice subassembly without a need for subsequent realignment of discharging ink flow stream or printer pattern.
Another specific feature of this invention is a continuous ink jet printer nozzle assembly having structures including a conduit defining an ink flow path and a sonic oscillator associated therewith, and one or more transverse bores terminating in close proximity to but isolated from the ink flow path and downstream from the oscillator suited to detect instantaneous properties of the ink stream flowing through the conduit, including the ink temperature and/or imparted sonic vibrations, etc., whereby such sensed feedback with suitable controls can vary power inputs to driver mechanisms including an ink heater/cooler and/or the sonic oscillator for maintaining a stable discharging ink flow stream or printer pattern.